Respiratory syncytial virus reinfections among infants and young children in the United States, 2011-2019.

Background: Although respiratory syncytial virus (RSV) immunoprophylaxis is recommended for high-risk infants, the American Academy of Pediatrics (AAP) recommends against immunoprophylaxis in the same season following a breakthrough hospitalization due to limited risk for a second hospitalization. Evidence in support of this recommendation is limited. We estimated population-based re-infection rates from 2011-2019 in children <5 years since RSV risk remains relatively high in this age group.

Materials And Methods: Using claims data from private insurance enrollees, we established cohorts of children <5 years who were followed to ascertain annual (July 1-June 30) and seasonal (November 1- February 28/29) RSV recurrence estimates. Unique RSV episodes included inpatient encounters with RSV diagnosis ≥30 days apart, and outpatient encounters ≥30 days apart from each other as well as from inpatient encounters. The risk of annual and seasonal re-infection was calculated as the proportion of children with a subsequent RSV episode in the same RSV year/season.

Results: Over the 8 assessed seasons/years (N = 6,705,979) and across all age groups annual inpatient and outpatient infection rates were 0.14% and 1.29%, respectively. Among children with a first infection, annual inpatient and outpatient re-infection rates were 0.25% (95% confidence interval (CI) = 0.22-0.28) and 3.44% (95% CI = 3.33-3.56), respectively. Both infection and re-infection rates declined with age.

Conclusion: While medically-attended re-infections contributed numerically only a fraction of the total RSV infections, re-infections among those with previous infection in the same season were of similar magnitude as the general infection risk, suggesting that a previous infection may not attenuate the risk for a re-infection.